Mobile electric leakage detection device and method

ABSTRACT

The present invention relates to a device and a method for, while moving, acknowledging the laying path of an electric line and simultaneously acknowledging the increasing point of ground potential, thereby being capable of updating information of the laying path of the electric line and simultaneously obtaining maintenance data. The present invention has developed a logic capable of classifying and determining a detection signal current when the detection signal current is distributed in several paths and flows according to association between multiple earthling of a neutral line and a new renewable energy source, and has specified a method for analyzing a signal generation and a signal reception for accurately distinguishing the magnetic field signal direction and logic.

TECHNICAL FIELD

The present invention relates to a mobile electric leakage locating andexploring device and method, more particularly, a mobile apparatus withmultiple wet type wheel electrodes contacting the earth to locate groundpotential increasing points while tracing laying paths of an electricline to acquire field information to update and repair, and a method forthe same.

BACKGROUND ART

Republic of Korea Patent No. 10-0778089 discloses an exploration systemand method for acquiring the field configured network information of anunderground low voltage (LV) distribution system, particularly in urbanareas where multiple transformers are grouped in a same location,including a plurality of master devices, a slave device and a detectingdevice. The plurality of master devices are connected to the terminalsof phases and earth inside of each of the transformers to broadcast theunique identification codes of a transformer, a phase and a circuit overthe feeding electric lines, the slave device acquires the information ofa source transformer, a connected phase and a circuit by reading thecodes in the broadcast or requests reply from the connecting point of anelectric line at a service entrance to a customer premise, and thedetecting device acquires the information of the source transformer, aphase and a customer by collecting a signal transmitted by the slavedevice in the middle of the laying path of the electric line withoutremoving the insulation while in service.

Republic of Korea Patent No. 10-0816101 relates to an earth voltageleakage sensing device and discloses the arrangement of a transmittingdevice and a receiving device to perform the task in service. While thetransmitting device applies a chain of asymmetrical pulse signals to apad mounted transformer, a stream of output signals fed by thetransformer to feeder cables are mixed signals of AC mains andasymmetrical pulse AC signals. The receiving device includes a signalinput part for gathering the earth voltage signals from the ground, afiltering part to eliminate the symmetrical voltage of AC mains andnoises from the signal inputs, a comparator part to compare the DCsignal polarity to display the + or − of the signal from the filteringpart, and an averaging part to average the value of accumulated DCsignal value from the filtering part in the specific period to displaythe signal value with the polarity from the comparator part, and picksthe asymmetrical pulse signal from the earth after removing thecommercial AC voltage wave from the detectable composite signal at theleaking point.

Republic of Korea Patent No. 10-0966759 relates to a method fordetecting and repairing a comprehensive streetlight power systemincluding a power cable from a utility and power distribution system toeach streetlight pole. The method includes performing an electricleakage diagnosis by measuring a resistive and capacitive leakagecurrent value under no load and full load conditions at a location wherecables stretched down from the utility pole run into a protective pipefor protecting the cables to determine whether an electric leakageoccurs in a street light power system when the resistive and capacitiveleakage current values are exceeding a threshold level, tracing anunderground cable from the utility pole to measure an electromagneticflux over the ground by increasing the sensitivity by step to detect anearth leaking point, and marking an earth leaking point by recordingdistances from landmarks.

In addition to above prior patents, New Technology #56 granted byMOKE(Ministry of Knowledge Economy) of Republic of Korea may bereferenced as a non-patent document(http://www.electricity.or.kr/ntep/search/search_view).

DISCLOSURE Technical Problem

FIG. 1 shows a series of photos while FIG. 2 shows a work flow chart toexplain an example of locating earth leaking points in the prior art.

Referring to FIGS. 1 and 2, the conventional method to locate an earthvoltage leaking point has 4 steps: (step 1) determining whether theearth voltage leaking happens to any of feeder lines fed by atransformer if more than 200 mA flows through a braided wire (Ig) whichbridges an earth ground (G) and a transformer winding neutral (Xo);(step 2) finding a suspicious earth leaking feeder line which carries avector sum current as much as said braided wire current (Ig) at thetransformer; (step 3) finding a suspicious earth leaking section in theroute of the said suspicious earth leaking feeder line; and (step 4)locating the earth leakage point on the ground within the saidsuspicious earth leaking section of the said feeder line.

The step 2 and step 3 for finding the suspicious earth leaking feederand the suspicious earth leaking section are conducted by detecting thecurrent vector sum (zero phase sequence current) (Io) shown in thephotos of FIG. 1, flowing through the 2 wires (phase+neutral) for asingle phase or 4 wires (A, B and C phases+neutral) for a three-phasesystem.

On the other hand, measures of the current vector sum (Io) at thestructures (joint places such as manhole) where a suspicious feeder linepasses through to find a first structure of the said current (Io)disappeared to determine the suspicious section between the laststructure with the leak current (Io) and the first one without it (Io)as step 3, to perform step 4 to locate the earth leaking point on theground within the said suspicious section, connect the asymmetricalpulse signal from the transmitting device to the terminals which isbetween the winding neutral (Xo) and the ground (G) after removing thebraided wire at the transformer, finalizing the earth leaking pointwhere the peak of the asymmetrical pulse signal by the receiving deviceas shown in FIG. 4, or determine that the earth leaking happens tocustomer's premise if the current vector sum (Io) is not disappeareduntil the end of the said feeder line.

In Some countries in North America and Republic of Korea, shown in theleft top corner of the FIG. 3, the primary and secondary winding centerpoints (neutral) of a distribution transformer are bonded and directlyearth grounded through the braided wire, Y-y directly earth grounded,but the neutral wire of the feeder lines and customer's premises areisolated from the earth ground. When an earth fault (leakage) happens toeither feeder lines or customer's premises, an earth fault currentshould return only to the transformer by a SGR (Source Ground Return)method. If the insulation of the feeder line is broken somewhere betweenthe structure 2 and structure 3, assume that the commercial voltage ofAC mains would leak out to the earth and return to the transformerthrough the earth resistance, creating a 0.5 A fault current (If) to theneutral point of transformer via the braided wire (Ig), and the zerophase sequence current (Ion) of 0.5 A at the feeder line which is sameas the fault (If). The braided wire (Ig) current would be extended tothe load side of structure 2 (Io2L) (If=Ig=Ion=Io1s˜Io2L) butdisappeared at the source side of structure 3 (Io3S), so the sectionbetween the structure 2 and structure 3 would be determined as asuspicious earth leaking section.

In FIG. 4, if the suspicious section of earth leaking is determinedsomewhere between manhole 1 and manhole 2, perform the earth leakingpoint accurate locating job to repair the earth faulted conductor wiresby an excavation work on the ground within the said suspicious sectionby picking a peak level of an asymmetrical pulse signal, which is a DC50V maximum, generated by a transmitting device connected to theneutral(Xo) wire and ground(G) after removing the braided wire at thetransformer by the receiving device which has sharp tip electrodes atboth ends thereof shown in FIG. 10.

An advantage of employing the SGR method is a simple mechanism todetermine whether an earth leakage happens to any feeder lines orcustomer premises by measuring the return fault ground current (Ig), butit also has a disadvantage that the leaking voltage would remainelectrically hazardous to the public if the earth resistance is not goodenough to discharge (return) the earth fault current where a place likefar end from the source.

Since a series of electric shock accidents occurred in 2005 due to theaforementioned disadvantage, Republic of Korea has introduced a newgrounding system, TNC defined by IEC Standard, which earths the neutralnot only at the source, transformer, but also at the structures in thefeeder lines, called PEN (Protective Earth Neutral), where multiple PENsare located both at a transformer and in the feeder lines to provide theadditional return paths to the earth leaking current to quickly clear upthe dangerous voltage by shortening the return distance to prevent theelectric shock accident.

However, there is no other new method or apparatus to detect the earthleaking under the introduced new grounding system. The conventionaltechnology judges mostly depending on currents at the transformer (Ig)and feeder line (Ion). FIG. 5 shows an example of earth voltage leakinghappening somewhere between the structures 2 and 3 under the TNCenvironment, where the earth fault current (If) of 1 A would no longerreturn to the transformer but to the nearest FED PEN2 which makes thefault returning current 0 A at the braided wire, such that theconventional method made wrong determinations that the feeder line whichhas 1 A earth leaking is healthy and thus could lead to abandonmaintenance, leaving electric shock dangers as high as possible topedestrians.

FIG. 6 shows an earth leakage happening at multiple points in a feederline, same as FIG. 5 where the two earth fault currents (If) would notreturn to the transformer, and thus return a fault current (Ig), and thezero-phase sequence current (Io) at the transformer could not bedetectable. Thereby, the judgment made by the currents measurement atthe transformer could not be correct to represent the true status ofearth leakage in the feeder lines. The only way to detect the true earthleaking feeder line and earth leaking section should be made bymeasuring the zero phase sequence current (Ion) at all the structuresalong the paths of the feeder lines go through. The earth leakingsections could be determined between manholes 1 and 2 (Io2), andmanholes 3 and 4 (Io4) of the feeder line.

But in real, an unbalanced phase load current returns through theneutral conductor wire to the source transformer like the earth faultcurrent (If). FIG. 7 shows some amounts of return load currents detouredaround another neutral conductor wire depending on the line impedanceand ampacity of the return load currents at the FED PEN.

That is, when the phase unbalanced return load current of 150 A flowsthrough neutral conductor wire 1 (N1) to the transformer 1 (TR1) whilethe 70 A of the returning load current goes through the neutralconductor wire 2(N2) to the transformer 2 (TR2), in the structure 2where two neutrals are non-grounded and used as a dedicated return pathto each transformer showing 0 A in zero phase current (Io) until thestructure 1 where neutrally grounded, the imbalance of flowing currentsin connections N1 and N2, a 15 A of current from N1 becomes detouredthrough the relatively lower current flowing N2 and reaches TR1 throughthe earth grounded neutral wire of medium voltage (MV) and the braidedwire of both TR1 and TR2 shown in FIG. 8, which could be a meaning of aleak current (Ig) in the conventional method. The detoured return loadcurrent of 15 A is treated as possible as a returning fault currentuntil finding a reason that the bypassed current at structure 1 afterstep 3 and step 4 are carried out, which is a manpower and budget waste.

Moreover, even if the braided wire current is from the true earth faultdetected by the conventional method to determine the suspicious sectionbetween the structures 1 and 2 shown in FIG. 9, the DC 50V ofasymmetrical signal is continuously transmitted using the conventionaltransmitting device to the neutral conductor wire of the feeder lineexpected to be leaked at a place of insulation fault, but the DC voltageleaks all over the PENs and returns to the ground of transformer beforearriving at the true leaking point, therefore the conventional methodcould not detect the earth leaking point and questioning whether thelocation of insulation failed neutral is always the same location offaulty phase conductor wires which carry the dangerous voltage riskunder the TNC earth system.

In addition, when assuming that the true earth voltage leaking happensin the feeder line 2 with a leaking current of 200 mA, the small earthfault current would be hidden by the big detoured current of 15 A, evenif it is successfully captured at the braided wire. But the conventionalmethod cannot distinguish the hidden one in the bigger current, and thuscan judge that the current is caused by the bypass current at thestructure 1 and close the investigation without finding a true earthvoltage leakage.

Technical Solution

Therefore, the present invention is such as to solve the conventionalproblems, using a method with a mobile earth leakage locating andexploring apparatus having multiple wet type wheel electrodes accordingto the present invention. The method includes: (1) tracing the layingpaths of phase conductor wires; (2) locating an increasing point of a ACmains earth potential; (3) locating a peak increasing point of a DCsurvey signal using polarity comparison when a logic value is ‘1’; and(4) identifying an earth leaking source by analyzing the logic values ofthe earth potential to provide a technology for accurately locating anexcavating position to repair the fault, also leaking source informationto enable to remove the dangerous voltage to prevent electric shockaccidents and equipment failure before civil works where an immediateaction is required.

In accordance with another aspect of the present invention, there isprovided a mobile ground potential scanning device including a pluralityof electrodes configured to be capacitively coupled to ground, aplurality of moisture supply means for supplying moisture to theplurality of electrodes and ground, and a potential measuring sectionfor measuring a plurality of earth potential values input from theplurality of electrodes.

Preferably, the electrodes may be in a form of wheels.

Preferably, the potentiometer may include a filter for extracting powerfrequency and harmonics.

Preferably, the mobile ground potential scanning device may furtherinclude a record section for recording a stream of data including theplurality of earth potential values at specific locations in accordancewith coordinate movements of the mobile detection device.

Preferably, the mobile ground potential scanning device may furtherinclude a map section for plotting a colored point in a coordinate planeon a map to represent the data in the record section.

In accordance with another aspect of the present invention, there isprovided a survey voltage signal transmitter including a diode; aresistor; a first connection wire connected to a hot (phase) wire of ACpower at a place; a second connection wire connected to a neutral wireof the AC power at the place; a switching unit for turning on and off acircuit connected between the hot wire and the neutral wire to control acurrent flow through the diode and the resistor connected in series; aswitching control unit for controlling a switch time of the circuit byproviding a time control signal to the switching unit to turn on thecircuit at a predetermined phase angle of the AC power and turn off thecircuit before a half wave extinction phase angle of the AC power; and acoding unit for controlling the switching control unit to whethergenerate the current flow or not and generating series of logic valuescorresponding to the current flow.

Preferably, the survey voltage signal transmitter may further include aninterface unit for synchronizing the switch time with an associateddevice through communications.

Preferably, the switching unit has three switching circuits to switch ifthe AC power has three phases.

The survey voltage signal transmitter may further include an input andsetting unit to enter identity information of the voltage transmitter tothe coding unit and set a single phase or three phases of the AC power.

In accordance with another aspect of the present invention, there isprovided a survey current signal transmitter to identify a burial pathof a power cable, the survey current signal transmitter including adiode; a resistor; a first connection wire connected to a hot (phase)wire of AC power at a place; a second connection wire connected to aneutral wire of the AC power at the place; a switching unit for turningon and off a circuit connected between the hot wire and the neutral wireto control a current flow through the diode and the resistor connectedin series; a switching control unit for controlling a switch time of thecircuit by providing a time control signal to the switching unit to turnon the circuit at a predetermined phase angle of the AC power and turnoff the circuit after a half wave extinction phase angle of the ACpower; and a coding unit for controlling the switching control unit towhether generate the current flow or not and generating series of logicvalues corresponding to the current flow.

Preferably, the survey current signal transmitter may further include aninterface unit to synchronize the switching time with an associateddevice through communications.

In accordance with another aspect of the present invention, there isprovided an accurate earth leak point survey apparatus including amagnetic field sensor; a plurality of electrodes configured to becapacitively coupled to ground; a signal timing unit for finding andsetting a time T by analyzing signals input from the magnetic fieldsensor, wherein the time T matches a signal start time of a surveycurrent transmitter; a signal detection unit for identifying a polarityand magnitude of a signal from the magnetic field sensor for apredetermined discrete period of time at a predetermined interval timefrom the time T; and a potential measuring unit for measuring an earthpotential value input from the plurality of electrodes.

Preferably, the potential measuring unit is synchronized with the time Tto identify the polarity and magnitude of the earth potential from theplurality of electrodes for the predetermined discrete period time atthe predetermined interval time from the time T.

Preferably, the signal detection unit is configured to simultaneouslyidentify the polarity and magnitude of the signal from each of theplurality of the magnetic sensors.

Preferably, the accurate earth leak point survey apparatus may furtherinclude an impedance selection unit for selecting a plurality ofimpedances and changing the values of impedances in parallel with theearth potential value.

Preferably, the potential measuring unit is configured to display earthleaking source information by reading a chain of logic values of theinput signals from the electrodes.

In accordance with another aspect of the present invention, there isprovided a method for detecting an electric leakage point of electricwires being supplied with power without interrupting such power supply,the method including moving a plurality of electrodes configured to becapacitively coupled to ground through moisture to record a stream ofdata including an earth potential at a respective location; anddetermining a suspicious area of electric voltage leakage by an electricwire of power supply.

In accordance with another aspect of the present invention, there isprovided another method for detecting an electric leakage point ofelectric wires being supplied with power without interrupting such powersupply, the method including transmitting a unipolar DC survey voltagesignal to an electric wire of the power supply; transmitting a chain ofelectromagnetic wave signals generated around the electric wire tosynchronize a reference time to measure an earth potential of theunipolar DC voltage signal and capture an electromagnetic trackingsignal; tracing a buried route of the electric wire by analyzing theelectromagnetic tracking signal according to the reference time;measuring the earth potential of the unipolar DC voltage signal on theground according to the reference time; and locating the electricleakage point by identifying a polarity of the unipolar DC voltagesignal.

Preferably, the method may further include measuring the earth potentialat the point on the ground determined as the electromagnetic trackingsignal at a location where a weaker electromagnetic signal detected inbetween two stronger oppositely signed electromagnetic signals.

Preferably, the method may further include analyzing informationcontained in the unipolar DC signal to identify a source of the electricleakage.

Advantageous Effects

According to embodiments of the present invention, an electric leakagedetection device and method employing a mobile ground potentialmeasurement device with water-supplied wheel-type electrodes have thefollowing effects.

First, a location where an AC commercial power ground potential isincreasing may be identified while the device quickly moves usingwater-supplied wet type wheel electrodes. Accordingly, an electricleakage position may be accurately identified without an error accordingto measurement of a zero-phase leakage current, and thus detectionreliability may be enhanced.

Second, a buried path of an electric wire may be accuratelydistinguished and detected to pinpoint an electric leakage point on theelectric wire having a hazard of electric shocks, and thus theexcavation position (the electric leakage point) can be accuratelylocated by measuring the AC commercial voltage ground potential and theDC voltage on the ground. Thereby, the electric leakage that may causeelectric shocks may be identified, and further the maintenance operationof the electric wire may be performed. Accordingly, accidents may beprevented.

Third, while two persons perform the path detection and measurement ofground potential separately in conventional cases, one person canperform the operations using the mobile ground potential measurementdevice, and use of the water-supplied wheel-type electrodes can savetime to move around. Accordingly, time for measurement may be shortenedand labor may be saved by storing and managing ground potential valuesfor respective positions.

Fourth, if it takes a long time to perform the excavation operation forfault recovery, temporary actions such as separation of a low-voltagecable exhibiting electric leakage from the power source may be takenbefore the excavation operation to eliminate the cause of electricshock. Thereby, maintenance costs may be saved.

DESCRIPTION OF DRAWINGS

FIG. 1 is a photograph showing a procedure of electric leakage detectionaccording to the conventional art.

FIG. 2 is a flowchart illustrating detection of electric leakageaccording to the conventional art.

FIG. 3 is a diagram illustrating detection of a suspicious electricleakage section of a non-grounded neutral low voltage (LV) cable used inthe conventional art.

FIG. 4 is a diagram illustrating detection of an electric leakage pointof a non-grounded neutral LV cable used in the conventional art.

FIG. 5 is a diagram illustrating detection of a suspicious electricleakage section of a neutral grounded LV cable used in the conventionalart.

FIG. 6 is a diagram illustrating detection of a multiple electricleakage points of a neutral grounded LV cable used in the conventionalarts.

FIG. 7 is a photograph illustrating a case of detection of a zero-phaseleakage current at a PEN of a neutral grounded LV cable (which is infact a case where the conventional device mistakenly detected a detouredcurrent on a neutral wire as a voltage leakage).

FIG. 8 is a diagram illustrating a detoured current at a PEN of aneutral grounded LV cable.

FIG. 9 is a diagram illustrating detection of electric leakage of aneutral grounded LV cable used in the conventional art.

FIG. 10 illustrates a probe with a ground contact electrode having asharp tip according to the conventional art.

FIG. 11 shows multiple switches and transformers installed at one placein an urban area.

FIG. 12 illustrates a block diagram to show medium voltage (MV) and LVfeeders, which are sharing a neutral wire in one system.

FIG. 13 is a circuit diagram illustrating detoured survey currentsignals at a PEN of a neutral grounded LV cable.

FIG. 14 illustrates a magnetic force relationship between 2 conductorsand a single conductor to carry the survey current signal.

FIG. 15 illustrates a horizontal sectional view of magnetic fields inFIG. 14.

FIG. 16 illustrates an arrangement of multiple magnetic field sensorsaccording to an embodiment of the present invention.

FIG. 17 illustrates a waveform of electromagnetic signals obtained overan underground duct with two opposite direction current flows.

FIG. 18 illustrates a waveform of electromagnetic signals obtained overan underground duct where a single polarity current flows.

FIG. 19 is a flowchart illustrating a logic to determine the directionsof buried paths of underground phase cables.

FIG. 20 illustrates a result of survey of an underground, buried path ofa couple of phase and neutral wires according to an embodiment of thepresent invention.

FIG. 21 illustrates a result of survey of an underground, buried path ofa neutral wire according to an embodiment of the present invention.

FIG. 22 illustrates metal wheel electrodes installed in a mobile groundpotential detection device according to an embodiment of the presentinvention.

FIG. 23 illustrates a wet type wheel electrode covered with a carbonfiber fabric according to an embodiment of the present invention.

FIG. 24 is a diagram illustrating configuration of a ground potentialmeasurement device for use in vehicles according to an embodiment of thepresent invention.

FIG. 25 is a block diagram illustrating a mobile ground potentialmeasurement device according to an embodiment of the present invention.

FIG. 26 illustrates configuration of a database of a mobile groundpotential measurement device according to an embodiment of the presentinvention.

FIG. 27 shows a database including details of the trajectory informationof FIG. 26.

FIG. 28 illustrates a map for marking ground potential value informationfor respective locations using colors according to an embodiment of thepresent invention.

FIG. 29 is a block diagram illustrating an accurate earth leak pointsurvey apparatus according to an embodiment of the present invention.

FIG. 30 is a photograph showing an example of an accurate earth leakpoint survey apparatus according to an embodiment of the presentinvention.

FIG. 31 illustrates an earth potential of AC commercial power voltagedetected on the ground from a neutral ungrounded LV cable.

FIG. 32 illustrates an earth potential of AC commercial power voltagedetected on the ground from a neutral grounded LV cable.

FIG. 33 is a photograph showing a measurement of electric leakage at aplace near a neutral grounded manhole.

FIG. 34 shows an earth potential of AC commercial power obtained at theplace of FIG. 33.

FIG. 35 is a circuit diagram illustrating a connection of a surveyvoltage and current transmitter to a neutral grounded LV distributionline.

FIG. 36 is a diagram illustrating a relationship between a surveyvoltage signal and a gate voltage of Insulated Gate Bipolar Transistor(IGBT) according to an embodiment of the present invention.

FIG. 37 is a photograph illustrating a DC survey voltage signalaccording to an embodiment of the present invention.

FIG. 38 is a photograph showing an enlarged view of a waveform of FIG.37.

FIG. 39 is a diagram illustrating a reason for which a DCvoltage-to-ground signal is generated only on a phase conductor wire.

FIG. 40 is a diagram illustrating a relationship between a surveycurrent signal and a gate voltage of IGBT according to an embodiment ofthe present invention.

FIG. 41 is a photograph showing a survey current signal and a gatevoltage together according to an embodiment of the present invention.

FIG. 42 is a diagram illustrating installation of an electric leakagedetection device including a survey voltage transmitter, a surveycurrent transmitter and an accurate earth leak point survey apparatusaccording to an embodiment of the present invention.

FIG. 43 is a flowchart illustrating a time synchronization inside anelectric leakage detection device shown in FIG. 42 according to anembodiment of the present invention.

FIG. 44 is a diagram illustrating a protocol for a time synchronizationinside an electric leakage detection device according to an embodimentof the present invention.

FIG. 45 is an internal circuit diagram illustrating a survey voltagetransmitter according to an embodiment of the present invention.

FIG. 46 is a block diagram illustrating a survey current transmitteraccording to an embodiment of the present invention.

FIG. 47 is a schematic circuit diagram illustrating an accurate earthleak point survey apparatus according to an embodiment of the presentinvention.

FIG. 48 illustrates a case where the accurate earth leak point surveyapparatus marks a direction before the electric leakage point.

FIG. 49 illustrates a case where the accurate earth leak point surveyapparatus marks a direction at the electric leakage point.

FIG. 50 illustrates a case when the accurate earth leak point surveyapparatus has passed the electric leakage point.

FIG. 51 is a photograph showing a DC survey voltage signal waveform atthe place of FIG. 33.

FIG. 52 is a photograph showing waveforms of earth potential of an ACcommercial power and a DC survey voltage signal together at the place ofFIG. 33 in a comparing manner.

FIG. 53 is a diagram illustrating a DC survey voltage signal generationtime for notifying magnetic field signal trigger time T and an actualmeasurement time according to an embodiment of the present invention.

FIG. 54 is a diagram illustrating a DC survey voltage signal measuringwindow open time and logic values according to an embodiment of thepresent invention.

FIG. 55 is a flowchart illustrating electric leakage detection accordingto an embodiment of the present invention.

FIG. 56 shows an example of accurate earth leak point survey apparatusseen from a view by a surveyor.

FIG. 57 shows 2 screens of a path detection and earth potentialmeasurement according to an embodiment of the present invention.

FIG. 58 shows a screen displaying a result of determination of thedirection of movement of a ground potential measurement device along aburied path of a power cable.

FIG. 59 shows a screen display for ground potential values from threewet type wheel electrodes in the accurate earth leak point surveyapparatus according to an embodiment of the present invention.

FIG. 60 is a diagram illustrating a menu item for changing internalimpedances of the accurate earth leak point survey apparatus accordingto an embodiment of the present invention.

FIG. 61 is a flowchart illustrating procedures how to reconstructelectromagnetic signals by the accurate earth leak point surveyapparatus according to an embodiment of the present invention.

FIG. 62 is a flowchart illustrating how to find the true time ‘T’ by theaccurate earth leak point survey apparatus according to an embodiment ofthe present invention.

BEST MODE

Reference will now be made in detail to the preferred embodiments of thepresent invention, examples of which are illustrated in the accompanyingdrawings. However, it should be noted that the present invention is notlimited or defined by the embodiments. Descriptions which are determinedto be apparent to those skilled in the art or redundant may be omitted.

In the Republic of Korea, the MV (Medium Voltage) and LV (Low Voltage)feeder lines are buried while the switch gears and transformers aregrouped on the ground in a place to reduce installation footprints inhigh density urban areas as shown in FIG. 11.

FIG. 12 shows a block diagram of the MV and LV feeder lines configuredin the area shown in FIG. 11 that 3 pad mounted transformers areconnected in series with a MV network through a SW1 or a SW2 at eachend. The figure shows that the MV is fed by SW1, and that eachtransformer steps down the MV to LV to supply AC mains to the endcustomers using the LV feeder lines which are installed in the samestructures with MV feeder line(s) sharing the earth ground rod. Themanhole 1 has 3 feeder lines including 1 MV and 2 LVs and 3 neutrals ofthe 3 different feeder lines jointed into an earth ground, which aresusceptible to detour a returning load current to another path mostlydepending on impedance and thus a flowing current could be highlyfallible to locate the earth leaking section by measuring a vector sumcurrent of a LV feeder in a system where a detoured neutral current iseasily made and causes a current vector sum value which might be treatedas a possible earth fault current to be investigated.

Thus, the present invention relates to an inventive technology whichdoes not measure a return current (Ig) and a zero phase sequence current(Io) in order to locate the earth leaking point like a conventionaltechnology, however it provides means to detect a rising point of the ACmains and a DC survey voltage signals on the ground while moving alongthe trajectory of the phase conductors (electric wires) of the feederlines and recording the earth potential in accordance with the locationdata.

The survey current signal to trace the buried route of feeder line willhave a same detoured returning phenomenon at the PENs like the returningload current does under the neutral ground environment when the surveycurrent signal generated by momentary switching between the phase andneutral conductor wires through a diode and resistors connected inseries by the survey current signal transmitter shown in FIG. 13, butthe strength of the radiated electromagnetic (EM) signal from thedetoured current is stronger than that from the feeder line to be tracedwhich causes major source of error in determining the route of bypassneutral route as that of the feeder line which has a risk of electricshock to be accurately traced.

FIG. 14 shows a vertical sectional view of ducts of feeder lines, wherethe direction of the magnetic field around the conductor wire isperpendicular to the direction of the survey current flowing with theright hand rule, the one duct where a phase conductor wire must betraced and associated with a neutral conductor has two electromagneticforce circles around each conductor wire in opposite directions to exertthe electromagnetic force to repel each other while the other duct withthe detoured neutral conductor wire has a uni-directional magnetic fieldcircle around the conductor wire without repulsion from the neighbors.

FIG. 15 are horizontal sectional views of the magnetic fields detectedon the ground, showing the characteristics thereof.

A nulling point of magnetism disposed between the conductor wires withthe different polarities makes a lower peak of the electromagnetic fieldas shown in section A-A′ when surveyed on the ground, but section B-B′has a full peak of the concentric circles of magnetic field in a singlepolarity direction over the detoured neutral conductor wire without anulling point as illustrated in the figure.

The repulsion between the phase and neutral conductor wires in the sameduct makes the surveyor to mistakenly believe the route of thee detouredneutral conductor wire as the phase conductor wire because the resultantof the electromagnetic fields from the latter is higher than that of theformer and because tracing the feeder line mostly depends on the peakstrength of the electromagnetic field over the ground to determine theroute of the buried route of the feeder line.

Previously, in the prior art considered, nothing other than the positionof the highest peak of the resultant of the magnetic field over theground as the laying position of the feeder line was used to detect thelocation of conductor wires because the survey current flows onlythrough the dedicated phase and neutral conductor wires of the feederline. But after all neutral conductor wires in a system are joined to anearth ground rod to be easily detoured through another neutral conductorwire, in the present invention, two factors are considered to accuratelytrace the hot (phase) conductor wire of the feeder line instead of thepeak detection at the points over the detoured neutral conductor. One iswhether a weaker electromagnetic signal space, such as a nullphenomenon, is detected between two stronger magnetic signals, andanother is whether the two stronger signals have opposite polarities asshown in FIG. 15, in order to implement the present invention bypositioning 4 ferrite coiled magnetic sensors 15 cm apart in horizonperpendicular to the direction of the buried route of the conductorwires as shown in FIG. 16 to catch the null of magnetism between thedifferent polarity signals at a position, preferably 20 cm above theground level to locate the duct where the phase and neutral conductorwires are disposed inside.

FIG. 17 shows 3 waveforms of the electromagnetic signals generated by asurvey current signal transmitter after removing the power frequency ofthe load current at a place directly over a duct containing phase andneutral conductor wires. Here, the arrangement of the electromagneticsensors are in horizon, each position of the sensors shown in FIG. 16 islinked to the waveforms, where the top waveform is from the left sensor({circle around (1)}), the middle waveform is from the right sensor({circle around (2)}), the last one at bottom is from the middle sensor({circle around (3)}). The polarity of the waveform on top from sensorat the left side is positive +, while the other two from the middle andright side sensors are same as negative −. The location of the buriedduct of the phase and neutral conductor wires is between the sensors ofthe different polarities {circumflex over (1)} (left) and {circumflexover (3)} (middle).

FIG. 18 shows the 3 waveforms over the duct of the detoured neutralconductor wire, where all of the three waveforms have all same polarityof +.

FIG. 19 is the flow charts of decision making to locate the phaseconductor wire by analyzing the polarity and amplitude simultaneously ofthe signals from the multiple sensors to determine the buried routeshown in FIG. 16. The highest priority of decision making is whether theincoming signals have the opposite polarities signals among the 4inputs, determine the position is directly over the duct of phase andneutral conductor wires when the incoming signals have a weaker levelcaused by cancellation like a null between the opposite polarities, andthen display an arrow to upward direction to move forward. For 2 pairsof same and opposite polarity signals without a space like a null amongthe inputs, the arrow against the same direction to move right orleftward is displayed. For 2 pairs of the opposite direction signalswithout a space, the arrow to a weaker opposite signal pair tohorizontal move will be displayed. For signals without opposite but samepolarities from the inputs, the arrow to a stronger sensor with a remarksaying the current location is over the duct without a phase conductorwire (detoured route) will be displayed.

FIG. 20 illustrates the survey result using the multi-sensor anddecision making logic to detect the polarity of the electromagneticsignals from the sensors as shown in FIG. 16 and the decision makinglogic to determine the each point as shown in FIG. 19 over the groundextending whole route of buried feeder lines by following the null ofthe magnetism between the opposite polarity sensors as shown in FIG. 25,while FIG. 21 shows all input electromagnetic signals having the singlepolarity of + which denotes a detoured neutral or water line without thephase conductor wire to trace.

The embodiment of the route survey apparatus comprising multi-sensorinputs to trace the route of a buried feeder line by picking up thepoints of the null between the opposite direction signals by thedecision making logic enables the surveyor to accurately locate thephase conductor wire which has potential to leak the dangerous voltageout to the earth instead of the zero potential detoured neutralconductor wire to prevent the electric shock accident by locating andremoving the earth leaking source.

The present invention also discloses the method and apparatus to locatethe earth leaking point by exploring the ground potential increasingpoint in which a leak is generated by any of degraded insulation of anelectric wire while moving along the buried route of the feeder lineusing the route survey apparatus and method mentioned above.

FIG. 10 shows a conventional portable earth potential device includingan A-shaped frame with 2 electrode legs. An electrode has ends with asharp tip to be forced down manually to the earth to minimize thecontact resistance every time while measuring the earth potential andthen a surveyor should walk to move the electrode along the feeder linewhich is a cumbersome and time consuming outside job. To speed up themeasuring job, in an embodiment of the present invention, a plurality ofmetal wheel electrodes made of cast iron shown in FIG. 22 are provided,such that the metal wheel electrodes are configured to detect the earthpotential increasing areas while rotating to move and directly touchingthe ground. However, in the above embodiment, the benefit of the newmethod of pushing the device with the metal wheel electrodes whichmeasure the leaked voltages was lesser than expected because foreignsubstances like soil debris and dirt easily can adhere to the surface ofmetal wheels to block the electrical conduction between the earth andmetal surface and furthermore the metal wheel may not have sufficientcontact areas. To improve once again the problems with the solid metalwheels, in another embodiment of the present invention, as shown in FIG.23, a metal conductor is wound up around an elastic vehicle tire andthen a carbon fiber fabric with durability like Velcro hook is disposedon the metal conductor. Further, water is sprayed over the fabric by apump, while moving along the route of the feeder line, such that thepump fed water can clean the dirt over the wheel and distribute theearth potential evenly over the fabric to measure the earth potential ofAC mains.

FIG. 24 is an example of an AC mains leakage scanning device forscanning wide areas, the device being attached to a SUV vehicle as atrailer equipped with multiple wet type wheel electrodes which arehorizontally and widely arranged to scan the AC mains earth potential toquickly search hazardous places in a metro area like and to store thesurvey results and travel trajectory in the server via wirelesscommunications.

FIG. 25 shows details of the wide area AC mains leakage scanning deviceto make production of the sample as shown in FIG. 24, driving thevehicle to follow the buried route map of the feeder lines or followingthe electromagnetic sensing signal to measure the values of voltage andcurrent of AC mains by the ground touching wet type wheel electrodes.FIG. 26 shows the contents of the sample database to be stored andmanaged including the values of voltage and current of AC mains between8 water fed wet type wheel electrodes, location data and weatherinformation, the reason that monitoring the voltage and current togetherwhile moving is simpler and quicker way to determine the increasedpotential is truly from the leakage of AC mains without stopping toverify the earth potential by changing the internal impedance.

It is another database of GPS trajectory of travel by the vehicle inFIG. 27, which is a location data link to the measuring valuesrespectively shown in FIG. 26.

FIG. 28 is the sample of the color plotting trajectory over the mapusing both database of measured value and coordinate movement data shownin FIGS. 27 and 28. The color of the each spot in the coordinate planeon the map represents the value of earth potential and current from thewet type wheel electrodes at the point of measured location.

After quick scanning of earth potential increasing area by the wide areaAC mains leakage scanning device to locate a suspicious earth leakingsection of AC mains possibly caused by a buried conductor wires of thefeeder lines which have a poor quality of insulation, conduct theaccurate earth leaking point survey at the area of suspicious earthleaking section to perform the maintenance job such as excavation torepair faulty conductor wires.

FIG. 29 shows an embodiment of the accurate earth leaking point surveyapparatus to pinpoint the accurate location of earth leaking point usinga push cart equipped with 3 wet type electrode wheels and moisturesupply means. After getting the results of the quick scanning the earthpotential increasing area by the wide area AC mains leakage scanningdevice shown in FIG. 28, an earth leaking point precision survey isfollowed by the hand push type accurate earth leaking point surveyapparatus at a suspicious location, when the time initiation protocoldescribed in FIG. 44 or non-repeating signal chains like ‘01010000’described in a flow chart in FIG. 61 as a true time ‘T’ generated by asurvey current signal transmitter. As soon as getting the time ‘T’, theaccurate earth leaking point survey apparatus resets a timer tosynchronize the time of signal creation and reading time between thesurvey current transmitter and accurate earth leaking point surveyapparatus to initiate the discrete period time and interval time tocatch both the electromagnetic signals over the ground by picking up thenull phenomenon between the two opposite polarities and the earthpotential increasing voltage of AC mains between the 3 wet type wheelelectrodes. As shown in FIG. 44, the incoming voltage signals from theelectrodes are filtered to pass the frequency between 30-300 Hz whichcan fully cover the AC mains voltage; then signal that the filteredsignal reached to the voltmeter(ADC) via an impedance logic, when aninput potential is higher than a threshold while connecting to thehighest value of impedance logic; verify that the increased potential iswhether truly leaked from the AC mains source if the voltage reading isstable even after lowering the value of impedance in 3 steps; locate thehighest potential increasing point of AC mains using the 3 electrodesdetecting job flow diagram shown in FIGS. 48-51; finalize the point ofhighest potential increase of AC mains using a DC survey voltageinjected into the conductor wires by comparing the direction of DCpolarity when the logic value is ‘1’; and find the leaking sources of ACmains by reading the information encoded in the DC survey voltage signalwithout excavation.

In brief, the job locating the earth leaking point has 4 steps to followin the suspicious area of earth leaking detected by the wide area ACmains scanner or without prior scanning as follows: (1) tracing theburied route of a phase conductor wire by collecting the polarities andmagnitude of electromagnetic signals over the ground; (2) locating theearth potential increasing point while tracing the buried route of thephase conductor wire; (3) finalizing the earth leaking point bycapturing the leaked DC survey voltage from a leak source of AC mains;and (4) finding the leak source by analyzing the codes in the leaked DCsurvey voltage on the ground.

The wide area AC mains leakage scanning device can scan the regionwithout tracing of the burial path of conductor wires, but can travelquickly along the expected burial route depending on the map to scan theearth potential voltage and current together using a plurality ofelectrodes in horizon which are wide enough to identify the suspicioussection where possibly earth leaking might be happening. After findingthe suspicious section of earth voltage leaking, the accurate earthleaking point survey apparatus can be used to accurately pinpoint thelocation of leaking source of AC mains while walking along the burialroute of phase conductor wires.

To locate the accurate point where the earth leaking is happening fromthe source of AC mains, a surveyor can walk along the points of nullsignals over the ground and measure the earth potential of AC mainsbetween the wet type wheel electrodes and stop at the place where theearth potential is exceeding the alert level to verify whether the inputpotential is truly leaking from the AC mains, if the point of the earthpotential elevated has a stable potential reading while impedance islowering, finalize that the point is the leaking point of AC mains whenthe DC survey voltage shows the same peak, and identify the AC mainsinformation by analyzing the DC survey voltage code to remove the earthleaking source without the civil works. To further improve the accuracyof survey, the present invention employs the time synchronizationbetween the accurate earth leaking point survey apparatus and DC surveyvoltage and DC current transmitter.

FIG. 30 shows an example of the accurate earth leaking point surveyapparatus explained above.

A vehicle includes a conductive metal wire spirally wound around theouter periphery of a rubber tire as an electrode to scan the earthpotential of the ground touched by the tire load and a water pump fedspray nozzle to remove the foreign substance on the surface of theelectrode and distribute the earth potential evenly around theelectrode. The vehicle can travel much faster than the conventionalelectrode which has sharp tips to be pressed manually at eachmeasurement location toward the ground while performing the task todetect the elevated location of earth potential. And furthermore thevehicle can store the earth potential and current information with therespective location data together into the server to be used formanaging and analyzing purposes.

In this way, the database stored in the server would be used whenconducting the analysis to view the trend of earth potential increasesat the point where the earth leaking is detected.

FIG. 31 shows the earth potential increasing level of AC mains near theearth leaking point where the neutral wire is not grounded and thus onlythe leaking voltage of AC mains is considered, which is not complex tofind a location around the single peak point, but the increasing levelof earth potential where the neutral wire is grounded and the multiplepeaks of earth potential are spread around the PEN, leaking point of ACmains (phase conductor wire) and another neutral return point (neutralconductor wire) are mixed together due to multiple return paths ofleaked and load currents shown in FIG. 32 and thus it is not easy tolocate the peak level of AC mains. FIG. 33 shows an earth leaking pointnear a manhole and a captured waveform of the earth potential shown inFIG. 34 between the manhole cover bonded to a neutral wire and the earthleaking point. The waveform of pure AC mains is hidden in the waveformof the multiple peaks, and thus it is not possible to catch the zerocrossing time to detect the peak level of the AC mains precisely.

In order to overcome these difficulties, when locating the earth leakingpoint of AC mains, caused from the distorted waveform shown in FIG. 34,it is preferred, in an embodiment of the present invention, to send a DCimpulsive survey voltage signal through the phase conductor wire toimprove the accuracy of survey to locate the earth voltage leakingpoint.

FIG. 35 shows a circuit drawing of a DC survey voltage transmitter whichcan generate the impulsive voltage signal shown in FIG. 36. This DCsurvey voltage transmitter is added to the feeder line to be surveyedtogether with the DC survey current transmitter shown in FIG. 13.Locating the earth leaking point by detecting the peak of the DC surveyvoltage could improve the accuracy of locating the AC mains peak.

The DC survey voltage transmitter configured to generate a half-wave DCvoltage signal between the phase and neutral conductor wires can beinstalled wherever close to the leaking point regardless a source orload side of the feeder line and adjustable to a single or a three-phaseconfiguration.

FIG. 36 shows a time chart to generate the half-wave DC survey voltagesignal. After applying the turn-on voltage to the gate of IGBT(Insulated gate bipolar transistor) by turning on a switch of thevoltage transmitter during the time of Tg, remove the applied voltage tothe gate of IGBT by turning off the switch momentarily to generate a bigimpulsive current (Ti) between the phase and neutral conductor wires. Atthe moment of cutting the flowing current sharply by removing the gatevoltage of IGBT as discussed above, a uni-polar transient voltage (Vp)occurs between the same conductor wires of current flow.

FIG. 37 shows a waveform of the DC survey voltage (transient voltage),which is the uni-polar and maximum voltage at an output terminal of thevoltage transmitter where the voltage is maintained under 320V byregulation. In Korea, the voltage range of AC mains is 220±13V and themaximum allowable peak voltage of AC mains should be less than 329V (233rms ACV*1.414).

FIG. 38 is the enlarged waveform of the DC survey voltage from the FIG.37. The gate turned on time of Tg is almost same as the current flowingtime (Ti) which is around 40 microsecond to generate the DC transientvoltage of about 320V maximum.

FIG. 39 shows a case where transmitting the uni-polar DC survey voltagesignal reversely when the DC survey voltage transmitter is connected toa neutral wire. A receiver in a vehicle mounted with an earth leakinglocator opens the measuring window of DC survey voltage signal at aspecific elapsed time between the positive slope zero crossing of ACmains and the firing time of IGBT. The top in the FIG. 39 shows thevoltage waveform of the AC mains and a DC survey voltage pulse just intime to match the logic value of ‘10’ between the transmitter and theearth potential locator (receiver). But the bottom shows a voltagewaveform reversed by 180 degree where, even the transmitter generatesthe DC survey voltage same as at the elapsed time from the zero crossing180 degree delayed, the voltage pulse generating time would not matchthe receiver's measuring time and finally the earth leaking locator(receiver) would fail to catch the signal pulse generated by thetransmitter. To guarantee the DC survey voltage signal to be deliveredto the receiver without an error, another time reference like the zerocrossing in the AC mains between the transmitter and receiver to locatethe DC survey voltage peak and identify the leaking source of AC mainsis needed.

FIG. 40 shows a time chart to generate a DC survey current signalcreated by a DC survey current transmitter shown in the left side ofFIG. 35, to synchronize the transmitting and measuring times between thetransmitter and receiver, and to minimize the measuring errors. Similarto the time chart of DC survey voltage shown in FIG. 36, except that theswitch off time of IGBT is after the negative slope zero crossing whichmeans the negative polarity of current is cut by the diode to minimizethe cut off surge voltage. When applying the turned-on voltage duringthe time of Tg to the gate of IGBT, the switch is turned on until a time(Ti) after the negative slope zero crossing time. A difference from thevoltage transmitter as shown in FIG. 36 is that the cut off transientvoltage would not be generated because the cutting voltage (Vp) isalmost 0V as the diode and the turned-on gate time (Tg) and the currentflowing time (Ti) are not same as in the voltage transmitter of FIG. 36.The characteristics of the survey current and voltage signals aredifferent not to interfere each other.

FIG. 41 shows a waveform of the DC survey current signal as an exampleunder the environment where a peak voltage of AC mains is 320V(226V*1.414) and a current limiting resistor of 2.5Ω in serial isincluded as shown in FIG. 35, firing the IGBT for 1.5 ms before thenegative slope zero crossing time, and where the measured voltage of ACmains is 174 Vp-p and the instantaneous peak current would be 65 A p-p[174V/2.67Ω (2.5+0.17 conductor resistance)] as a survey signal at thefiring time and decreased 0 A to be extinguished after 1.5 msec as shownFIG. 41.

V _(t) =V _(peak)*Sin(wt+Φ)

Φ=((8.33 ms−1.5 ms)/8.33)*180=147⁰

If the current limiting resistor is 2.0Ω, then the current would beincreased up to 147 A p-p instantaneously. When Vt=174 V, the currentsignal instantaneous value is about 65 A (including conductor resistanceof 0.17Ω). If a resistor having resistance of 2.0Ω is selected forgeneration of a current signal, an instantaneous current signal of about147 A is generated.

If the IGBT is turned on to flow the fixed current (65 A) and is thenturned off to cut off the flow current before the extinction time wouldcreate the transient surge voltage like a DC survey voltage as shown inFIG. 36, but turning off the IGBT after the extinction time wouldgenerate only the DC survey current without the voltage as shown in FIG.40.

But the waveform of the AC mains collected from the leaking point isdistorted as shown in FIG. 32 or FIG. 34 which is not easy to extractthe zero crossing time to be used as synchronizing the signal generationand receiving (measuring) times between the transmitter and receiver(locator). If the times of sending and receiving are not matching eachother as shown in FIG. 39, the locator could not detect the DC surveyvoltage signal at all.

In order to solve this problem that is to detect the DC survey voltagesignal correctly even when the waveform of AC mains is distorted not tobe able to provide the reference time to measure such as the zerocrossing, it is preferred to synchronize the transmitting and receivingtimes between the transmitter and locator (receiver) without dependencyof AC mains as described in FIG. 43. The procedure to detect the DCsurvey voltage on the ground requires the 3 devices shown in FIG. 42,including (1) the DC survey voltage transmitter and (2) DC surveycurrent transmitter both connected to the feeder line to be surveyed,and (3) the accurate earth leaking point survey apparatus configured todetect the earth potential increasing location of AC mains from the wettype wheel electrodes while moving along the path of phase and neutralconductor wires flowing the DC survey current by following the series ofelectromagnetic signal null sensing points between the oppositedirections. This procedure includes the steps of: (1) exchanging thefiring time of the DC survey voltage signal between the transmitters ofDC survey voltage and DC survey current; (2) notifying the measuringtime to the accurate earth leaking point survey apparatus in the form ofelectromagnetic signal from the DC survey current transmitter; (3)detecting the earth potential of the DC survey voltage signal on theground by the accurate earth leaking point survey apparatus aftersetting the new measuring time by collecting the electromagneticsignals; and (4) in addition to the detection of the leaking point, theaccurate earth leaking point survey apparatus identifying the earthleaking source information to prevent an electric shock accident withoutthe excavation work.

FIG. 44 illustrates the protocol exchange process among the DC surveyvoltage transmitter, the DC survey current transmitter and the accurateearth leaking point survey apparatus to synchronize the time and matchthe time to generate and detect the signal. The DC survey voltagetransmitter sends an initiation code to each phase in sequence waitingfor reply from the DC survey current transmitter to know which phase isconnected. As example, the DC survey current transmitter replies atphase B. After getting reply from phase B, the DC survey voltage signaltransmitter sends continuous measuring signals through the phaseconductor B to locate the DC survey voltage signal by the accurate earthleaking point survey apparatus, to get the electromagnetic signal totrace the phase conductor and synchronize the measuring time to detectthe DC survey voltage signal on the ground while tracing the route ofphase conductor which carrying the DC survey voltage signal.

FIG. 45 shows a block diagram of the DC survey voltage transmitter,which has an interface part to exchange the time of the DC surveyvoltage signal generated with the DC survey current transmitter, a phaseselecting part to choose a single or 3 phases, an input part to set aself-ID of the accurate earth leaking point survey apparatus, a DCsurvey voltage generating part which generates current pulses as a timecharacteristic and generates the transient voltage as shown in FIG. 36at every 120 degree angle time in sequence, a coding part for assigningvalues of meaning (logic values) to the DC voltage pulses. Since theamount of transfer energy by DC survey voltage signal is proportional tothe amount of currents flowing through the gate as shown in FIG. 36, thephase angle of the gate voltage can be adjusted closer to the top of thesign curve corresponding to the maximum voltage such that the surveyvoltage transmitter can generate a higher survey voltage when thecurrent is momentarily disconnected.

FIG. 46 shows a block diagram of the DC survey current transmitter whichhas a power cable interface part to connect the transmitter to the ACmains, and a diode for rectifying the input AC into a half waveuni-polar voltage and generating a current pulse with a timecharacteristic shown in FIG. 36 so as to generate a DC survey currentsignal to send electromagnetic signals to be traced and to besynchronized with the measuring time of the accurate earth leaking pointsurvey apparatus. This device is configured to coordinate the signalsbetween the DC survey voltage transmitter and accurate earth leakingpoint survey apparatus to improve the accuracy of the survey without thedependency of zero crossing time of AC mains.

FIG. 47 shows a block diagram of the accurate earth leaking point surveyapparatus which has 3 main functions including an earth potentialdetection function of AC mains, an earth potential detection function ofDC survey voltage, and a buried route tracing function by detectingelectromagnetic signals.

Firstly, the earth potential detection function of AC mains requires 3inputs from the wet type wheel electrodes with a pump fed water spraynozzle while moving on the ground to trace the buried route of the phaseconductor wire touching the ground to scan the earth potentials of ACmains to detect potential increasing locations. The 3 inputs from theelectrodes pass the input selection switch and are filtered by a BPF inthe range of 40˜300 Hz within the frequency of AC mains to reach the ADCvia an internal impedance selecting switch to verify the input of earthpotential is truly from the potential leak of AC mains. It is preferredto set the highest value of the internal impedance as infinite, to moveand stop at a location where the potential is more than 50 mV and makesure the reading of potential is maintained in a stable level even theimpedance is changed to a lower value.

After finding a peak location of earth potential of AC mains by usingone of wet type wheel electrodes or A-frame tip electrodes, a moreaccurate peak of the earth potential of the DC survey voltage on theground around the peak location of AC mains can be precisely detected.The measuring time and route tracing signals are in the form ofelectromagnetic signals in the air from the DC survey current signaltransmitter.

The input signal of DC survey voltage will pass through a high passfilter of 15 kHz to the ADC via a fixed internal impedance of 10 MΩ forexample. When the signal level of the DC survey voltage signal needs tobe changed, the firing time of IGBT (Tg) should be shifted as shown inthe FIG. 36. The DC survey voltage signals also have the information ofthe earth leaking source transmitted by the DC survey currenttransmitter which could be useful to isolate the earth leaking sourcewithout excavation in emergency situations.

Moreover, the accurate earth leaking point survey apparatus has afunction of acquiring geospatial data from the IMU, GPS and odometerfrom the wheel rotation counter, etc., and a communication unit to storethe acquired data into the server through a communication medium.

FIG. 48 shows earth potential levels of AC mains from the 3 wet typewheel electrodes to reach the earth leaking point to display an arrowupward to go forward to the leaking point where V2 (V2=|V2−V3|) is lowerthan V1 (V1=|V1−V2|) and V3 (V3=|V3−V1|).

FIG. 49 shows earth potential levels of AC mains detected directly overthe earth leaking point and displays a circle shown just over theleaking point where all 3 values of V1, V2 and V3 have a same minimumvalue.

FIG. 50 shows an earth potential detected at a location after passingthe leakage point of FIG. 49, where the value of V2 is higher than thoseof V1 and V3, and illustrates a downward arrow to imply that the leakingpoint is behind the current location.

The earth potentials of AC mains among the 3 wet type wheel electrodesare compared and analyzed in such a way that, before and after the earthleaking point, the value of the potential suddenly is increased ordecreased but, directly on the earth leaking point, the value becomesthe lowest in all 3 electrodes, i.e., the point having the lowestpotential value can be determined as a leaking point.

FIG. 51 shows a waveform of the DC survey voltage signal received at theearth leaking point shown in FIG. 33, and the FIG. 52 shows both anearth potential voltage in FIG. 34 and a DC survey voltage in FIG. 51 tocompare the waveform between the AC mains and DC survey voltage.

The waveforms between the earth potential of AC mains with a 40˜300 Hzrange and DC survey voltage signal with a 15 kHz above range are notwell matched in the timing and amplitude of the peak because the lowfrequency of AC mains and mixture of potential created by other returnload will have more distortion (time shift) compared to the waveform ofthe DC survey signal. Therefore finalizing the earth leaking point onlyafter doing the peak detection of the earth voltage of AC mainssometimes could be erroneous result.

FIG. 53 shows an example of implementation of time intervals between anotification time from the DC survey current transmitter to the accurateearth leaking point survey apparatus and an actual measuring time todetect the earth potential of DC survey voltage, which is a ⅓ cycle ofAC mains. If the DC survey current transmitter sends the notification tothe accurate earth leaking point survey apparatus in the form ofelectromagnetic signals, after a successful reception of thenotification signal, the accurate earth leaking point survey apparatuswill do the measuring of the DC survey voltage the ⅓ cycle time later atthe time a logic value is ‘1’.

After getting the notification time signal from the DC survey currenttransmitter, the accurate earth leaking point survey apparatusautomatically opens a measuring window to measure the earth potential ofthe DC survey voltage on the ground the ⅓ cycle of AC mains later asprogrammed.

FIG. 54 shows the opening time of measuring window and earth potentialof the DC survey voltage signal together with the logic value of‘00110’. The accurate earth leaking point survey apparatus measures theearth potential of DC survey pulse within the time of measuring windowopen to distinguish the signal from noise, and when the earth potentialsignal exists in the time of measuring window open, set the logic valueas ‘1’, otherwise ‘0’.

FIG. 55 shows a flow chart to locate an earth potential leaking point.As shown in the case of FIG. 42, the survey current and voltagetransmitter are connected to a LV cable to be examined. To perform theaccurate survey of earth leakage point, trace along the buried route ofphase conductor wires using the accurate earth leak point surveyapparatus. Alternatively, drive along expected routes of buried cablesto roughly scan the earth potential increasing (unsafe) places in acertain wide area where underground distribution feeder lines areinstalled by using the AC mains leakage scanning device with themultiple wet type wheel electrodes, and then pinpoint the accuratelocation of earth leaking and acquire the leaking cable informationwithin said earth potential increasing (unsafe) places.

FIGS. 56 and 57 show an example of the accurate earth leaking pointsurvey apparatus viewed from the hand pushing location and 2 screens toallow one operator to perform tracing the path of a buried phaseconductor wire and measuring the increasing point of ground potential atone time, comprising a plurality of wet type wheel electrodes to measureground potential, a moisture supply means, multiple magnetic fieldsignal sensors, and a water tank and a water hose for continuouslysupplying water to reduce a contact resistance between the electrodesand the ground.

FIG. 58 shows 4 input electromagnetic signals with polarities andmagnitudes received from the electromagnetic sensors shown in FIG. 29,where a null (which has the magnitude closer to zero) is at the 3^(rd)place from the leftist between the opposite polarities (+ in the 2ndfrom the leftist, − in the rightest), so that the place corresponding tothe location of null position is determined to be directly over theroute of a duct which includes phase and neutral conductor wires to betraced, and thus an arrow is displayed direct a surveyor to moveforward.

FIG. 59 shows a screen display indicating 3 ground potential values V1,V2 and V3 input from the wet type wheel electrodes.

FIG. 60 shows a screen to judge the true ground potential leakagedistinguished from an induced false voltage at an alarmed location wherethe ground potential is exceeding a threshold level by connecting adifferent internal impedance to the measuring circuit shown in FIG. 47.

FIG. 61 is a flowchart illustrating a procedure how the accurate earthleak point survey apparatus measures the electromagnetic signals. Tominimize an influence of a load current, it is configured to have theload current pass a filter of 600 Hz and be digitized. And, reconstructsampled signals similar to the survey current signal in a period andsequence and pass them through the signal authenticity logic as shown inFIG. 62. Thereafter, when a trigger time T is determined by the signalauthenticity logic, the true time ‘T’ is used as a synchronized time tomeasure the polarity and magnitude of the electromagnetic signal.

Referring to FIG. 62, the logic of identifying the true time ‘T’ basedon the unknown inputs from the electromagnetic sensors includesaveraging 16 sampled signals to reconstruct a signal to have a samediscrete period time and put them in sequence distanced by a powerfrequency 1 cycle interval (16.7 msec if 60 Hz) to detect a series oflogic values from the chain of recovered signals that is not a repeatedlogic value of ‘0’, and following additional ‘1000’ logic value to bedetermined as the true time T′ and resetting the time ‘T’ in FIG. 61identical to the measuring time.

FIG. 63 illustrates a record section in the wide area AC mains leakagescanning device in detail. The record section provides the location datacombining gathered data from the GPS, IMU (Inertial Measurement Unit)and odometer from a wheel electrode to enable to spot an accurate pointon the map with the value of measurement.

It is preferred to transmit input signals from the 4 EMF sensors into afilter which has a center frequency 600 HZ to eliminate electromagneticsignals with a certain power frequency range so as to minimize theinfluence from the load current flowing in a power cable to be traced,and then the filtered signals are digitized by a sampled 19,200 Hz rate.To transform a signal to have a same discrete period time (1.5 msec) ofsurvey current signal, average or pick the maximum value in the 16samples (0.8 msec), and find a logic value chain of the recoveredelectromagnetic signal which has the same value of the initiation codeof survey current signals to determine the true time ‘T’ as thesynchronized reference time to compare the polarity and magnitude ofelectromagnetic signal to find the buried point of electric power lineand measure the earth potential according to the time, and record themeasured data with the location data from a satellite into the recordsection in the accurate earth leak point survey apparatus.

Although the preferred embodiments of the present invention have beendisclosed for illustrative purposes, those skilled in the art willappreciate that various modifications, additions and substitutions arepossible, without departing from the scope and spirit of the inventionas disclosed in the accompanying claims.

1. 1 A mobile electric leakage detection device comprising: a plurality of electrodes configured to be capacitively coupled to ground; a plurality of moisture supply means for supplying moisture to the plurality of electrodes and ground; and a potential measuring section for measuring a plurality of earth potential values input from the plurality of electrodes.
 2. The mobile electric leakage detection device according to claim 1, wherein the plurality of electrodes are in a form of wheels.
 3. The mobile electric leakage detection device according to claim 1, wherein the potential measuring section includes a filter unit configured to extract power frequency and harmonics.
 4. The mobile electric leakage detection device according to claim 1, further comprising a record section for recording a stream of data including the plurality of earth potential values at specific locations in accordance with coordinate movements of the mobile detection device.
 5. The mobile electric leakage detection device according to claim 4, further comprising a map section for plotting a colored point in a coordinate plane on a map to represent the data in the record section.
 6. A survey voltage transmitter comprising: a diode; a resistor; a first connection wire connected to a hot wire of AC power at a place; a second connection wire connected to a neutral wire of the AC power at the place; a switching unit for turning on and off a circuit connected between the hot wire and the neutral wire to control a current flow through the diode and the resistor connected in series; a switching control unit for controlling a switch time of the circuit by providing a time control signal to the switching unit to turn on the circuit at a predetermined phase angle of the AC power and turn off the circuit before a half wave extinction phase angle of the AC power; and a coding unit for controlling the switching control unit to whether generate the current flow or not and generating series of logic values corresponding to the current flow.
 7. The survey voltage transmitter according to claim 6, further comprising an interface unit for synchronizing the switch time with an associated device through communications.
 8. The survey voltage transmitter according to claim 6, wherein the switching unit has three switching circuits to switch if the AC power has three phases.
 9. The survey voltage transmitter according to claim 6, further comprising an input and setting unit to enter identity information of the voltage transmitter to the coding unit and set a single phase or three phases of the AC power.
 10. A survey current transmitter configured to identify a burial path of a power cable, comprising: a diode; a resistor; a first connection wire connected to a hot wire of AC power at a place; a second connection wire connected to a neutral wire of the AC power at the place; a switching unit for turning on and off a circuit connected between the hot wire and the neutral wire to control a current flow through the diode and the resistor connected in series; a switching control unit for controlling a switch time of the circuit by providing a time control signal to the switching unit to turn on the circuit at a predetermined phase angle of the AC power and turn off the circuit after a half wave extinction phase angle of the AC power; and a coding unit for controlling the switching control unit to whether generate the current flow or not and generating series of logic values corresponding to the current flow.
 11. The survey current transmitter according to claim 10, further comprising an interface unit to synchronize the switching time with an associated device through communications.
 12. A mobile earth leaking survey apparatus comprising: a magnetic field sensor; a plurality of electrodes configured to be capacitively coupled to ground; a signal timing unit for finding and setting a time T by analyzing signals input from the magnetic field sensor, wherein the time T matches a signal start time of a survey current transmitter; a signal detection unit for identifying a polarity and magnitude of a signal from the magnetic field sensor for a predetermined discrete period of time at a predetermined interval time from the time T; and a potential measuring unit for measuring an earth potential value input from the plurality of electrodes.
 13. The mobile earth leaking survey apparatus according to claim 12, wherein the potential measuring unit is synchronized with the time T to identify the polarity and magnitude of the earth potential from the plurality of electrodes for the predetermined discrete period time at the predetermined interval time from the time T.
 14. The mobile earth leaking survey apparatus according to claim 12, wherein the signal detection unit is configured to simultaneously identify the polarity and magnitude of the signal from each of the plurality of the magnetic sensors.
 15. The mobile earth leaking survey apparatus according to claim 12, further comprising: an impedance selection unit for selecting a plurality of impedances and changing the values of impedances in parallel with the earth potential value.
 16. The mobile earth leaking survey apparatus according to claim 12, wherein the potential measuring unit is configured to display electric-line information showing a chain of potential leakages by capturing the input signals from the electrodes.
 17. A method for detecting an electric leakage point without interrupting a power supply, the method comprising the steps of: moving a plurality of electrodes configured to be capacitively coupled to ground through moisture to record a stream of data including an earth potential at a respective location; and determining a suspicious area of electric voltage leakage by an electric wire of power supply.
 18. A method for detecting an electric leakage point without interrupting a power supply, the method comprising the steps of: transmitting a unipolar DC survey voltage signal to an electric wire of the power supply; transmitting a chain of electromagnetic wave signals generated around the electric wire to synchronize a reference time to measure an earth potential of the unipolar DC voltage signal and capture an electromagnetic tracking signal; tracing a buried route of the electric wire by analyzing the electromagnetic tracking signal according to the reference time; measuring the earth potential of the unipolar DC voltage signal on the ground according to the reference time; and locating the electric leakage point by identifying a polarity of the unipolar DC voltage signal.
 19. The method according to claim 18, further comprising: measuring the earth potential at the point on the ground determined as the electromagnetic tracking signal at a location where a weaker electromagnetic signal detected in between two stronger oppositely signed electromagnetic signals.
 20. The method according to claim 18, further comprising: analyzing information contained in the unipolar DC signal to identify a source of the electric leakage. 